Transmittance and refresh rate are important indexes for liquid crystal displays. Transmittance refers to the amount of the backlight after passing through a liquid crystal panel, and refresh rate refers to the frequency for liquid crystal charging. The increasing of the transmittance can improve the brightness of a display, and reduce costs. The increasing of refresh rate can improve the quality of dynamic images, depress tailing and reduce costs.
Current techniques of wide viewing angle horizontal electric field comprise IPS (In-Plane-Switching) and FFS (Fringe Field Switching). IPS has an adverse impact on transmittance because a metallic material is used for the pixel electrodes in an array substrate; and FFS cannot meet the developing market requirement, since the storage capacitance is so large that the refresh rate can only reach up to 120 Hz.
An array substrate of a conventional FFS structure comprises a common electrode layer 5′, a pixel electrode 2′, a glass substrate 3′ and a protective layer 10′. Voltage difference is applied across the common electrode layer 5′ and the pixel electrode 2′, generating an electric field 4′, but the electric field 4′ does not comprise a horizontal electric field component, which gives rise to an insufficient driving force for driving liquid crystal molecules above the pixel electrode 2′. Therefore, a higher arrangement density is necessary for the pixel electrodes so as to remedy the defect of insufficient driving force for the liquid crystal molecules. However, if the arrangement density for the pixel electrodes is increased, the transmittance will be reduced.
In the aspect of structural design, the controlling force of the electric field acting on liquid crystal determines the transmittance of the liquid crystal. Generally, the electrodes are greater than 3 μm in width. The electric field always performs control on the liquid crystal molecules generally at edges of electrodes, whereas the portions over the electrodes tend to be the positions where the electric field force is the weakest and accordingly the liquid crystal molecules have low transmittance, which causes an overall reduction of the transmittance. The same problem also happens to the FFS configuration. Although a transparent ITO (Indium Tin Oxide) material is employed for the pixel electrodes, the overall transmittance is adversely impacted as the transmittance of the liquid crystal above the pixel electrodes is not high. While in FFS configuration, the pixel electrodes will create greater storage capacitance with the lower common electrodes, which on one hand benefits the stabilizing of the pixel voltage, and on the other hand, the FFS configuration shows significant insufficiency in its application during recent years, and as more and more products call for high refresh rate. 3D techniques, integration technology and so on require support from a higher refresh rate; while greater storage capacitance causes a longer charging period for the pixels in FFS configuration, leaving a decreased refresh rate.